FACTORS INFLUENCING THE UTILIZATION OF REDUCED NICOTINAMIDE ADENINE DINUCLEOTIDE BY PIGEON HEART MITOCHONDRIA

Abstract

Pigeon heart mitochondria that were studied exhibited ADP:O and respiratory control ratios of 2.3–3.1 and 6–20 respectively with glutamate as substrate. This coupled respiration of glutamate was reversibly inhibited by ATP. In polarographic and photometric experiments at 28° in a medium containing 0.23 M mannitol, 0.07 M sucrose, 0.02 M Tris, and 0.02 mM EDTA at pH 7.2 such mitochondria oxidized 15–150 μM NADH with essentially zero order kinetics and an apparent Kmof approximately 4 μM. NADH oxidation, which was not coupled to phosphorylation, was increased 50% by the addition of 5 mM orthophosphate (Pi) but was inhibited by albumin, NAD, ATP, and ADP. The effect of NAD became marked only at concentrations of 2–5 mM. However, ATP in concentrations (5–10 mM) similar to those found in heart, inhibited by 50–75% the oxidation of physiological levels (~ 10 μM) of NADH. These and other findings are compatible with the view that the oxidation of cytoplasmic NADH is a normal property of heart mitochondria, and that the control of this process by changes in the intracellular levels of ATP and Pimay influence myocardial carbohydrate utilization.